You can skip commercials with Tivo-like devices. Also commercials come in fixed time lengths, it's very easy to manually scan past them. Since the overwhelming majority of TVs and home theater systems are remote controlled, the changing volume just isn't a big concern - you use the remote to change the volume. Philips applied for a patent earlier this year for a TV that freezes it controls whenever a commercial starts so you can't change the channel or the volume. They have no plans to implement this feature since they see no consumer demand for it.
